1. Field of the Invention
The present invention relates to a serial bus interface device to be connected to a next-generation digital interface typified by the IEEE 1394 serial bus. More particularly, the invention relates to a serial bus interface device suitable as a bus analyzer for checking a communication state on a bus such as an IEEE 1394 serial bus, operations of a device connected to the bus, and the like.
2. Description of Related Art
A next-generation digital interface typified by the IEEE 1394 serial bus is used not only for data transfer between a personal computer and a peripheral device of the personal computer but also for transfer of multimedia data such as moving picture data between a digital AV device such as a digital camera or a DVD player and a personal computer and between digital AV devices. The digital interface is therefore requested to have a high data transfer speed. The application range of the digital interface includes ordinary households. Consequently, what is called a plug-and-play function which can deal with the insertion or withdrawal of a device in a power-on state is necessary.
The IEEE 1394 serial bus has a high data transfer speed such that a packet transfer speed is 100 to 400 megabits per second and supports two kinds of transfer modes: a synchronous transfer mode for stable transfer of multimedia data; and an asynchronous transfer mode for transferring conventional-type data and the like. In order to realize the plug-and-play function, the IEEE 1394 serial bus has a function of reconstructing the topology by executing an initial sequence when a device is inserted or withdrawn, and automatically assigning an identification number (ID) to each device.
For example, as shown in FIG. 1, in order to analyze the communication state between a personal computer 101 (ID=1) and a digital camera 102 (ID=0) which are connected via an IEEE 1394 serial bus B, it is necessary to allow a bus analyzer 100 to receive packets on the bus B. For this purpose, a construction that the bus analyzer 100 has a physical layer circuit compliant with the communication protocol of the IEEE 1394 standard is achieved by inserting the bus analyzer 100 on the bus B connecting the personal computer 101 and the digital camera 102. Specifically, the personal computer 101 and the bus analyzer 100 are connected via a bus B1 and the bus analyzer 100 and the digital camera 102 are connected via a bus B2. The IEEE 1394 serial bus reconstructs a bus topology, assigns a new ID (=1) to the bus analyzer 100 via a physical layer circuit, and recognizes the bus analyzer 100 as a device connected to the buses B1 and B2. After the bus analyzer 100 is incorporated into the IEEE 1394 serial bus and the communication on the buses B1 and B2 becomes possible, the bus analyzer 100 analyzes the communication state between the personal computer 101 and the digital camera 102. In this case, since the ID is simultaneously reassigned to an existing device, the personal computer 101 is recognized as a device having the ID of 2 in place of the ID of 1.
FIG. 2 shows a case where (n+1) devices are connected on the serial bus and a method of analyzing the communicating operation, for example, on a bus BB of a device A (ID=0) in an IEEE 1394 serial bus system comprising devices A to H (IDs=0 to 7) and other devices (IDs=8 to n). A case of, for example, analyzing the communicating operation of the device A such as a newly-developed hard disk drive which is connected to the bus is assumed. The bus BB connecting the device A (ID=0) and the device B (ID=4) is divided into a bus BB1 and a bus BB2, and the bus analyzer 100 having a physical layer circuit is inserted between the buses BB1 and BB2. In this case as well, in a manner similar to the case of FIG. 1, the IEEE 1394 serial bus reconstructs the bus topology, recognizes the bus analyzer 100 as a device having the ID of 1, resets the IDs of the other devices, and constructs an IEEE 1394 serial bus in a state where the bus analyzer 100 is incorporated. The communications on the buses BB1 and BB2 become possible and the bus analyzer 100 analyzes the communicating operation of the device A.
In order to analyze the communicating state between the personal computer 101 and the digital camera 102, however, the serial bus interface device used as the bus analyzer 100 shown in FIG. 1 has to be inserted in the bus B connecting the personal computer 101 and the digital camera 102 via the physical layer circuit. By inserting the bus analyzer 100, the bus analyzer 100 itself becomes one of the devices on the bus. Consequently, the bus configuration has a topology including the bus analyzer 100 which does not exist in an inherent connection environment. It causes a problem such that analysis in a communication environment in the inherent topology cannot be performed.
Further, in the serial bus interface device used as the bus analyzer 100 shown in FIG. 2, in a manner similar to the case of FIG. 1, by inserting the bus analyzer 100, the configuration of buses changes and it causes a problem such that analysis in a communication environment in the inherent topology cannot be performed.
When the communicating state of a bus has to be analyzed in a state where a number of devices are connected to the bus, it is necessary to connect all the devices so as to be adapted to a regular use environment and then analyze the communicating state. When the analysis has to be performed in a state where there are a number of devices to be connected or a number of kinds of devices, there is a problem such that enormous efforts are required to set an analysis environment.